An experimental vaccine for Lassa fever, a viral haemorrhagic illness endemic to parts of West Africa, has commenced its first human trials in the United Kingdom. This marks a significant step towards improved prevention for a disease that causes recurrent annual outbreaks, particularly in Nigeria. The vaccine's development is a collaborative effort by researchers at the University of Oxford, a UK-based institution, with crucial support from the Coalition for Epidemic Preparedness Innovations (CEPI).

CEPI, a global health organization, plays a vital role in funding vaccine development for epidemic-prone diseases. Katrin Ramsauer, CEPI's Lassa programme lead, highlighted that Lassa fever, first identified in 1969, has long been neglected in vaccine development due to its primary impact on low- and middle-income countries, which presented limited commercial incentives for pharmaceutical companies. Survivors often endure severe long-term complications, including hearing loss and neurological problems, and the true disease burden is likely underestimated. CEPI was established in the wake of the 2014-2016 Ebola outbreak specifically to bridge this gap by supporting vaccines with high public health impact but limited market appeal.

The initial clinical trial, a Phase One study, is currently underway in the UK and is designed to rigorously assess the vaccine's safety in healthy adult volunteers. Maheshi Ramasamy, an infectious disease specialist at the University of Oxford, reported that six healthy volunteers aged 18 to 50 have already received the experimental vaccine. The vaccine utilizes the well-established ChAdOx1 platform, a viral vector technology also employed in the globally administered Oxford-AstraZeneca COVID-19 vaccine, which boasts an extensive safety record with billions of doses used worldwide. All participants are reported to be doing well, with no serious adverse events. Reported side effects have been mild and transient, mirroring those associated with routine vaccinations, such as temporary arm pain, fatigue, and headaches. The trial aims to enroll an additional 25 participants in the UK and approximately 50 in Ghana before progressing to larger Phase 2 trials, which are expected to include Nigeria.

Addressing the decision to initiate early trials outside Nigeria, Ms. Ramsauer explained that early-stage clinical trials are typically conducted in locations with well-established research infrastructure to ensure utmost safety and expedited progress. She underscored Nigeria's pivotal role in Lassa fever vaccine research, noting that the country is already hosting other CEPI-supported Lassa fever vaccine studies, including a Phase two trial by another developer. CEPI has made significant investments in bolstering clinical trial capacity within Nigeria to facilitate vaccine research, and while the Oxford-led candidate began in the UK, it is planned to move to Ghana for further early-stage testing before advancing to later phases in Nigeria and other West African nations.

Oyeronke Oyebanji, who leads CEPI's Lassa fever engagement in West Africa, emphasized the organization's proactive efforts to foster community trust and ensure equitable access to any future vaccine. In partnership with the West African Health Organisation, CEPI established the Lassa Fever Coalition, involving Nigeria, Liberia, Sierra Leone, Guinea, and the Benin Republic. This coalition serves as a collaborative platform for governments, scientists, and policymakers to strategically plan vaccine development, future introduction, pricing, and availability. Furthermore, CEPI is funding social science studies in Nigeria, Liberia, and Sierra Leone to gain deeper insights into vaccine hesitancy, willingness to participate in clinical trials, and community perceptions regarding Lassa fever vaccines, demonstrating a commitment to early engagement and understanding of local contexts.

Ms. Ramasamy clarified that the experimental vaccine is designed as a preventive tool to protect individuals from Lassa fever infection, not as a treatment for those already infected. She also stressed the critical importance of developing multiple vaccine candidates to ensure resilience in supply and manufacturing, citing lessons learned from the COVID-19 pandemic regarding the risks of over-reliance on a single vaccine. Having diverse effective vaccines enables a faster response and broader protection of various populations during outbreaks.

Lassa fever, a rodent-borne viral disease, primarily spreads to humans through exposure to food, water, or household items contaminated by infected rats. Human-to-human transmission can also occur through contact with bodily fluids. The illness often presents with non-specific initial symptoms like fever and weakness, which can delay timely care-seeking. However, it can progress rapidly to severe complications, including bleeding, respiratory distress, and organ failure, if not treated early.

In Nigeria, Lassa fever remains a persistent and serious public health challenge. According to the Nigeria Centre for Disease Control and Prevention (NCDC), as of epidemiological week 51 of 2025, the country had recorded 206 deaths from Lassa fever. The case fatality rate (CFR) had risen to 18.4 percent, an increase from 16.4 percent observed during the same period in 2024, despite a decline in the number of confirmed cases during the reporting week. Specifically, between December 15-21, 2025, Nigeria reported 21 new confirmed cases across seven states (Bauchi, Ondo, Taraba, Edo, Kogi, Ebonyi, and Plateau), down from 28 cases the previous week. However, five deaths were recorded among these confirmed cases, resulting in a weekly CFR of 23.8 percent.

Cumulatively for 2025, Nigeria reported 1,119 confirmed cases, nine probable cases, and 9,270 suspected cases across 21 states and 105 local government areas. While this represents a decrease in total confirmed cases compared to 2024 (1,237 confirmed cases), the NCDC attributed the increase in fatalities (206 deaths in 2025 versus 203 in 2024) largely to late presentation at health facilities. The states of Ondo (contributing 35 percent), Bauchi, Edo, and Taraba collectively accounted for 88 percent of confirmed cases in 2025. The NCDC identified several critical factors contributing to the rising fatality rate, including late health-seeking behaviour, high treatment costs, inadequate environmental sanitation, and low awareness within high-burden communities.